He said the investigation would look into what munitions were used and how they were deployed.

A senior White House official told the BBC that the investigation will focus on whether US-made weapons were used against non-military targets.

Washington has supplied Israel with cluster bombs since the 1970s, on the understanding that they would only be used against defined military targets.

'Balconies and roofs'

The UN's Mine Action Coordination Centre says it has found 318 sites in south Lebanon where cluster bombs have been used.

"A lot of them are in civilian areas, on farmland and in people's homes, said spokeswoman Dalya Farran.

"We're finding a lot at the entrances to houses, on balconies and roofs," she said.

"Sometimes windows are broken and they get inside the houses."

"Most of them are from America," Ms Farran said.

According to the UN, eight Lebanese have been killed and at least 30 wounded by exploding ordnance left behind after the 14 August ceasefire between Israel and Hezbollah came into force.

Hezbollah tactics

Although cluster bombs themselves are not illegal under international law, many human rights groups believe their use in populated areas violates the prohibition on indiscriminate attacks contained in the Geneva Conventions.

The Israeli army said all weapons it uses were "legal under international law and their use conforms with international standards".

A congressional investigation after Israel's invasion of Lebanon in 1982 found Israel guilty of intentionally dropping cluster bombs in civilian areas.

A six year ban was imposed on further sales of the weapons to Israel.

But a senior White House official told the BBC that the current investigation is unlikely to lead to any serious repercussions.

Throughout the recent conflict, Israel argued that it tried to minimise civilian casualties.

But it said that Hezbollah fighters had hidden rocket launchers in houses, blurring the distinction between civilian and military targets.